1. Technical Field
The present invention relates to a heating flow path unit which is mounted on a liquid ejecting head such as an ink jet recording head and a liquid ejecting head including the heating flow path unit. In particular, the invention relates to a heating flow path unit having a plurality of liquid flow paths which are arranged in parallel and a liquid ejecting head including the heating flow path unit.
2. Related Art
As a representative liquid ejecting head, for example, an ink jet recording head (hereinafter, referred to as recording head) which is mounted on an ink jet printer (one type of liquid ejecting apparatus, hereinafter, referred to as printer) can be exemplified. The ink jet printer performs recording by discharging and landing ink in a liquid form onto a recording medium (ejected target) such as a recording paper. Further, the liquid ejecting heads are used for ejecting various types of liquids other than ink. For example, a color material used for a color filter such as a liquid crystal display, an organic material used for an organic Electro Luminescence (EL) display, an electrode material used for forming an electrode, and the like are ejected from the liquid ejecting heads.
In recent years, photocurable ink which is cured with irradiation of light energy such as ultraviolet rays is used when an image or the like is printed in some case. The photocurable ink is cured and fixed to even a recording medium having poor ink absorbency by irradiating the photocurable ink with light. Therefore, the photocurable ink is used for recording an image onto a resin film, for example, and other various applications. However, the photocurable ink tends to have viscosity higher than that of common aqueous ink. For example, the viscosity of the aqueous ink at a normal temperature (for example, 25° C.) is lower than 8 mPa·s. On the other hand, the viscosity of the photocurable ink at the normal temperature is equal to or higher than 8 mPa·s. The viscosity of the ink is required to be made lower in order for such ink in a so-called high viscosity range to be ejected by the liquid ejecting head. Therefore, there has been proposed a liquid ejecting head which is configured to eject ink onto a recording medium after the viscosity of the ink has been made lower to a viscosity suitable for being ejected by heating the ink with a heating unit such as a heater (for example, see JP-A-2009-083470).
In the invention as disclosed in JP-A-2009-083470, a heating flow path unit having a liquid flow portion which allows communication between flow paths of a liquid supply source (self-sealing valve) and a recording head is provided therebetween. Further, in the invention as disclosed in JP-A-2009-083470, ink passing through the liquid flow portion is heated with a heater so as to lower viscosity of the ink. A main body (base body) of the heating flow path unit is a hollow block member formed by a material having high heat conductivity such as a metal. An internal space of the main body is divided by dividing walls so that a plurality of liquid flow portions are formed in parallel. With this configuration, heat from the heater is transferred to the ink flowing through the liquid flow portions through the unit base body including the dividing walls. With this configuration, ink can be heated while suppressing a flow path resistance and a pressure loss from increasing.
Flow rates of inks flowing through the plurality of liquid flow paths which are formed in parallel are not necessarily constant depending on a position of an opening of a flow path provided at the upstream side or the downstream side with respect to the liquid flow paths. That is, a flow rate of ink flowing through the liquid flow portion formed at a position close to the opening of the flow path provided at the upstream side or the downstream side is relatively high. On the other hand, a flow rate of ink flowing through the liquid flow portion formed at a position distanced from the opening of the flow path provided at the upstream side or the downstream side is relatively low. In general, the liquid flow portion formed at a center portion among the liquid flow portions is the closest to the opening of the flow path provided at the upstream side or the downstream side. Therefore, a flow rate of ink flowing through the liquid flow portion formed at the center portion is higher than flow rates of inks flowing through the liquid flow portions formed at ends. As the flow rate is higher, time taken for ink to pass through the liquid flow portion becomes shorter. Therefore, there has arisen a problem that ink passing through the liquid flow portion in which flow rate is high is hard to be heated sufficiently.